1. Field of the Invention
The present invention relates to a CRT (Cathode Ray Tube), and more particularly, to a CRT, in which lengths of vertical axes (Y-axes) of outermost row slots of a long side of a shadow mask, slots adjacent to the outermost row slots in a central direction of the shadow mask and slots adjacent to the adjacent slots in a central direction of the shadow mask are maintained in the range of 70%xcx9c110% of a length of a vertical axis (Y-axis) of a perfect slot, thereby providing a visually stable screen.
2. Description of the Background Art
As shown in FIG. 1, a conventional CRT (Cathode Ray Tube) includes a fluorescent surface 4 of R, G and B colors coated on an inner surface thereof, a panel 1 having a front surface on which an explosion-proof glass is fixed, a funnel 2 fused to a rear end of the panel, an electron gun 3 inserted into a neck part 12 of the funnel and emitting electron beams 10, a shadow mask 5 mounted on an inner surface of the panel in a regular interval and having a plurality of holes for passing the electron beams, a frame 6 fixing and supporting the shadow mask and for maintaining the shadow mask in the regular interval from the inner surface of the panel, an inner shield 11 for shielding the CRT so as to reduce effects from the earth""s magnetism, and a reinforcing band 7 mounted on the circumference of a side part of the panel for preventing external shock.
Reference numeral 8 indicates a deflection yoke and reference numeral 9 indicates a spring.
As shown in FIG. 2, the shadow mask of the Background Art includes an effective surface 13 having a plurality of round or oval holes for passing electron beams 10 emitted from the electron gun 3, and a skirt part 14 partially etched and having a prescribed length for welding the frame supporting the shadow mask.
Referring to FIG. 3a, when the electron beams 10 emitted from the electron gun 3 pass the holes formed in the effective surface 13 of the shadow mask and strike the fluorescent surface 4 coated on the panel 1, a plurality of slots 15 of a fixed size are arranged horizontally and vertically in regular intervals to maintain the electron beams 10 in regular intervals. Bridges (B) are formed between the adjacent slots 15 in regular intervals to maintain the intensity after forming the shadow mask.
The CRT of the Background Art having the above structure has an inner surface of the panel having a curvature, and the shadow mask also has a curvature. Therefore, to give the effective surface the appearance of a flat rectangular shape when a user sees a screen, shapes of long and short sides of the effective surface of the shadow mask are calculated geometrically and manufactured in the form of a pin or a barrel.
It is not difficult to manufacture the short side of the shadow mask into a desired shape even though a horizontal interval (Ph) of the slots 15 is changed, but it is very difficult to manufacture the long side of the shadow mask by changing a vertical interval (Pu). This is due to vertical wave patterns.
Therefore, lengths of a vertical axis direction (Y-axis) of the outermost row slots of the long side of the shadow mask are made to differ according to the effective surface. Thereby, because a shape of a long side end of the screen formed during an exposure process in a color CRT a convexo-concave shape is formed on upper and lower portions of the screen during the luminescence of the screen, thereby deteriorating the grade of the screen.
Referring to the drawings, the above problems will be described in more detail as follows:
As shown in FIG. 3a, when the outermost row slots formed along the long side, are formed in the convexo-concave shape, the shape of the end of the vertical axis direction of the screen formed during the exposure process is the convexo-concave form shown in FIG. 4. In the exposure process of the color CRT, an exposure device performs the exposure operation in the vertical axis direction to form graphite stripes on the inner surface of the panel. Thus, if the slots are more than a prescribed size, the light passing the slots of the shadow mask having the convexo-concave shape forms the graphite stripes of the same shape on the inner surface of the panel, and thereby the end of the effective surface of the screen has the convexo-concave shape during the luminescence of the screen. To remove the convexo-concave shape of the end of the effective surface, non-luminescent material must be coated on the stripes formed during the exposure process.
As shown in FIG. 3b, when the bridges between the outermost row slots of the vertical axis direction of the shadow mask and slots adjacent to the outermost row stats are removed and the slots are connected to the end of the effective surface and exposed, the effectual surface of the screen can have a straight line without the convexo-concave shape. However, as described later, the outermost row slots of the vertical axis direction of the shadow mask, in which the outermost row slots and the slots adjacent to the outermost row slots are connected and expanded, have a larger shadow mask transmissivity mask than other adjacent slots, which are not connected. Thus, the electron beams passing the slots are formed relatively large on the screen, and thereby continuous white spots are formed on the end of the effective surface of the screen according to the difference in brightness of the electron beams between the outermost row slots arranged in the vertical axis direction of the shadow mask and the adjacent slots during the luminescence of the screen by the electron beams. Two equations are provided below.
Shadow Mask Transmissivity
=area of slot/(horizontal interval of slotsxc3x97vertical interval of slots) Shadow Mask Transmissivity in the case of connecting the outermost row slots and the adjacent slots
=(area of outermost row slots+area of the adjacent slots+area of bridges)/(horizontal interval of slotxc3x97vertical interval of slot)
When the bridges between the outermost row slots and slots positioned underneath the outermost row slots, which are located in the vertical axis direction of the shadow mask, are removed and the slots are connected to the end of the effective surface thereof, the portion where the slots are connected becomes lower in shadow mask intensity than a portion where the slots are not connected, when a curved surface of the effective surface of the shadow mask is formed, thereby causing a droop of the slots after the forming process of the shadow mask.
Moreover, if the slots of the same row number are formed in an entire area from the center of the shadow mask toward the periphery of the shadow mask by changing the vertical interval of the slots, vertical wave patterns may be formed on the screen due to an interference phenomenon between a scanning interval of the electron beams and the vertical interval of the slot.
It is, therefore, an object of the present invention to provide a CRT(Cathode Ray Tube) capable of preventing a formation of a convexo-concave shape on upper and lower portions of a screen during the luminescence of the screen by maintaining lengths of outermost row slots arranged in a vertical axis direction of a shadow mask, slots adjacent to the outermost row slots in a central direction of the shadow mask and slots adjacent to the adjacent slots in a central direction of the shadow mask in the range of 70xcx9c110% of a length of a vertical axis (Y-axis) of perfect slots.
It is another object of the present invention to provide a color CRT capable of removing continuous white spots generated on an end of an effective surface by removing bridges between the outermost row slots arranged in the vertical axis direction of the shadow mask and slots arranged underneath the outermost row slots and by connecting the slots to the end of the effective surface and preventing stains of a periphery of the screen generated by short slots, thereby providing a visually stable screen.
To achieve the above objects, the present invention provides a color CRT including a panel having a luminescent screen on an inner surface thereof, a funnel connected to the panel, an electron gun mounted on a neck part of the funnel, the electron gun emitting electron beams toward the luminescent screen, a shadow mask disposed in a fixed interval to the luminescent screen formed on the inner surface of the panel, the shadow mask serving to select colors, and a frame fixing and supporting the shadow mask, wherein the shadow mask includes an effective surface having a plurality of slots and a non-effective surface surrounding the effective surface; wherein the slots includes first slots on an outermost row arranged in a vertical axis direction of the effective surface of the shadow mask, second slots being adjacent to the first slots in the vertical axis direction, third slots being adjacent to the second slots in the vertical axis direction, and fourth slots being adjacent to the third slots in the vertical axis direction; and wherein a length of the vertical axis direction of the first slots is in the range of 70%xcx9c110% of a length of the vertical axis direction of the fourth slots.
A length of the vertical axis direction of the second slots is in the range of 70%xcx9c110% of a length of the vertical axis direction of the fourth slots, and a length of the vertical axis direction of the third slots is in the range of 70%xcx9c110% of a length of the vertical axis direction of the fourth slots.